Page:Aspects of nature in different lands and different climates; with scientific elucidations (IA b29329668 0002).pdf/44

 *[Footnote: in two estimable English journals. (Compare my Asie Centrale, T. iii. p. 262, with Hooker, Journal of Botany, vol. i. 1834, p. 327, and Edinburgh New Philosophical Journal, vol. xvii. 1834, p. 380.) The Saxifrage discovered by Boussingault is certainly, up to the present time, the highest known phænogamous plant on the surface of the earth.

The perpendicular height of the Chimborazo is, according to my trigonometrical measurement, 3350 toises (21422 E. feet.) (Recueil d'Observ. Astron., vol. i., Introd. p. lxxii.) This result is intermediate between those given by French and Spanish academicians. The differences depend not on different assumptions for refraction, but on differences in the reduction of the measured base lines to the level of the sea. In the Andes this reduction could only be made by the barometer, and thus every measurement called a trigonometric measurement is also a barometric one, of which the result differs according to the first term in the formula employed. If in chains of mountains of great mass, such as the Andes, we insist on determining the greater part of the whole altitude trigonometrically, measuring from a low and distant point in the plain or nearly at the level of the sea, we can only obtain very small angles of altitude. On the other hand, not only is it difficult to find a convenient base among mountains, but also every step increases the portion of the height which must be determined barometrically. These difficulties have to be encountered by every traveller who selects, among the elevated plains which surround the Andes, the station at which he may execute his geodesical measurements. My measure-*]*